When determining paving quantities, resurfacing grades, side-road tie-in grades, or making other design decisions, roadway design engineers must know the elevations of the roadway at three important locations of the roadway profile. These are the left edge of the pavement, the crown point, and the right edge of the pavement.
Presently, the most economical way for surveyors to gather this information is by using a total station package in which a device including a theodolite, an electronic distance meter and an electronic data collector is fixed over a known ground control point. The horizontal coordinates and elevation of the desired points on the roadway profile are determined by sighting light reflecting prisms which are positioned at the top of poles of controlled heights. Using this conventional scheme, a high level of accuracy may be achieved relatively quickly and efficiently in obtaining the necessary data.
However, as traffic volumes increase due to population growth and related factors, it is becoming more difficult and hazardous for surveyors to access elevation measurements in the middle of the roadway. In some cases injury to the surveyor or vehicle occupant results. In some instances time consuming roadway closures are the result. In other cases, the design engineer may be forced to complete the project without the benefit of crown point elevations at all.